The present invention relates to methods for improving cheese production by utilizing plasmin-regulating agents to maintain plasmin in the animal's milk at levels less than 0.2 mg/l milk. All animals whose milk is used to produce cheese benefit from the administration of the plasmin-affecting agents of the present invention. For instance, milk from cows, sheep, goats or even buffalo, to name a few, is used in cheese production. One such compound is bovine somatotropin (hereinafter referred to as BST).
Plasmin is a component of an animal's blood and appears to be involved with fibrinolysis primarily. However, plasmin also has been implicated in cell migration and differentiation, involution of the uterus and mammary gland. Often times, plasminogen activator is synthesized by the target tissue in order to generate localized plasmin production.
Plasmin interacts with milk and cheese in a very particular manner. It seems that milk plasmin increases in late lactation resulting in the increased formation of gamma caseins from the proteolysis of alpha-s and beta casein (Donnelly, 1983). Observed at the same time is an increase in plasminogen activator during natural mammary gland involution or during hormonally induced involution in cell culture. Such an increase in plasminogen activators may be speculated to increase plasmin concentrations with a subsequent degradation of milk proteins.
Recently, an increase in bovine milk plasmin has been observed in late lactation. Further, bovine milk also fluctuates in milk plasmin concentrations depending on the season of the year. Generally, in the spring plasmin and plasminogen are lower, and in the winter plasmin and plasminogen seem to be higher. Additionally, during mastitis or during periods of elevated somatic cell counts, milk plasmin seems to be increased. The decrease in the integrity of the alveslar epithelia within the mammary gland results in an increased transfer of blood plasminogen/plasmin to milk.
Proteolysis of kappa-casein is necessary in cheese production. However, excess non-specific proteolyisis reduces firmness when cheese is being produced. In the more neutral pH cheeses, such as swiss cheese, plasmin is highest, and it is lowest in the acid cheeses such as cheshire cheese. Plasmin degrades beta casein into three components. Also, plasmin has been reported to induce gelation of ultra high temperature pasteurized milk. The formation of amino acids during cheddar cheese ripening yields production of bitter flavors in milk and dairy products and decreasing cheese yield and quality. If milk is incubated with plasmin longer than four hours there is a resulting increase in time necessary to form a rennet clot which is necessary in cheese production.
Difficulties in cheese production from milk exposed to increased levels of plasmin concentration are observed due to seasonal calving in some parts of the world, and therefore, a method to increase cheese production is desireable and will allow cheese manufacture help in such areas of cheese shortages. If milk is processed 1 to 3 days after it is collected from the cow, obviously a high level of plasmin coupled with long incubation time will degrade the alpha-s and beta caseins thereby reducing cheese yield. External modulators which can minimize fluctuation in plasma concentration over lactation or prevent plasmin increases during diseases (mastitis) have tremendous potential in insuring consistent milk for cheese processing and results.
Surprisingly, it has been observed that with injections of recombinant bovine somatotropin (BST), as an example of a plasmin-regulating agent, milk plasmin concentrations observed in late lactations revert to those of early lactation, i.e., the milk plasmin concentration decreases. Thus, a method to improve cheese production yields by administering compounds which decrease milk plasmin levels is provided herein.